Photographic materials which have good original reproduction characteristics, stable development baths and simple replenishment are some of the requirements in the field of photomechanical process for dealing with the diversity and complexity of printed matter.
Original documents in line work processes are made with a paste-up of photoset text, hand written text, illustrations and screened photographs. Hence, the original documents comprise a mixture of images of different densities and line widths, and there is a consequent demand for process cameras, photographic materials and methods of image formation which reproduce these original documents with a good finish. Further, enlargement (spread) or reduction (choke) of screened photographs is widely used in plate making for catalogues and posters. In plate making where screen dots are enlarged, the number of lines becomes coarser and blurred dot reproduction occurs. With reduction, the number of lines per inch is greater than on the original document and finer dots are reproduced. Hence, there is a demand for a method of forming images which has a wider latitude in maintaining the reproducibility of the original screen gradation.
Halogen lamps or xenon lamps are used as the light source for process cameras. Photographic materials are normally ortho sensitized to achieve photographic sensitivity to these light sources. However, ortho sensitized photographic materials are greatly affected by chromatic aberration of lenses and this aberration is likely to result in a deterioration of picture quality. This deterioration is more pronounced with xenon lamp light sources.
Known systems developed in response to the demand for wider latitudes include those in which line images or dot images (in which there is a clear distinction between image parts and non-image parts and which have high contrast and high black densities) are obtained by processing lith type silver halide photographic materials comprising silver chlorobromides (in which the silver chloride content is at least 50 mol %) in hydroquinone developers containing a very low effective concentration of sulfite ion (normally not more than 0.1 mol/liter). However, with these methods the developer is very unstable with respect to aerial oxidation because of the low sulfite concentration, though various endeavors and devices have been used to maintain a stable bath activity. Further, processing is very slow and operational efficiency is reduced.
Consequently, a demand has arisen for image forming systems in which the instability of image formation (caused by development methods such as (lith development systems) are overcome, with which development is carried out in processing baths having a good storage stability, and with which superhigh contrast photographic characteristics can be realized. In these systems superhigh contrast images of a gamma value exceeding 10 are formed by processing surface latent image type silver halide photographic materials to which specified acylhydrazine compounds have been added. Processing is performed in development baths of a pH from 11.0 to 12.3, containing at least 0.15 mol/liter of sulfite preservative, and having good storage stability, suggested in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606 and 4,311,781. A distinguishing feature of these novel image forming systems is that, whereas only silver chlorobromides which had a high silver chloride content could be used in the conventional superhigh contrast image forming systems, silver iodobromides and silver chloroiodobromides can also be used in these novel systems.
The above mentioned image forming systems provide excellent sharp screen dot quality, processing stability, processing speed and original reproduction characteristics. But systems which provide still better original reproduction characteristics have become desirable for dealing with the diversity of printed matter.
Attempts have been made to widen the gradation reproduction range by using photographic materials which contain redox compounds which release photographically useful groups on oxidation as shown in JP-A-61-213847 and U.S. Pat. No. 4,684,604. However, with superhigh contrast systems in which hydrazine derivatives are used, the hydrazine compounds have the adverse effect interfering with the hardening of contrast and the required characteristics cannot be realized.